P-type metal oxide semiconductor transistor (PMOS) devices are utilized throughout the electronics industry. Source/drain regions of transistors are generally formed in the substrate over which the transistor gate is formed. The source-drain structures can be formed of a strain inducing material in order to introduce strain in the channel region of the transistor. PMOS performance is enhanced by applying compressive strain to the channel, whereas NMOS performance is improved by tensile strain. The increased strain is known to improve device performance and device speed.
One method for applying compressive strain involves epitaxial growth of silicon on top of a silicon-germanium underlayer in the source-drain regions. The lattice of the silicon layer is stretched to follow the larger lattice constant of the underlying silicon-germanium. This causes compression of the channel.